This invention is directed to a cooling device for controlling the temperature of a projection lamp in an image projector and, more particularly, to a control for the cooling device.
Portable image projectors are becoming more popular and desirable. Some of the portable projectors are small enough and light enough to be carried by one hand and are generally referred to as xe2x80x9cultra-portable.xe2x80x9d The image projector typically includes a lamp module removably housed inside the image projector. Some of these portable image projectors may include a lamp module that uses a metal-halide arc lamp which operates at a very high temperature and requires a high voltage pulse to ignite the arc. The arc lamp may be part of a lamp module unit. These portable projectors must be compact and lightweight, and must be packaged to protect users and the projector from heat, high voltage, and improper operating modes, such as operation of equipment at excessive temperatures, and high-voltage pulse generation during arc lamp replacement. In particular, the compactness of the units combined with the high temperatures of the high intensity lamps make controlling the heat produced by the arc lamps very important.
The arc lamp operates at a low temperature during an initial start-up period and, after the arc is established, gradually warms up to its full operating temperature. Initially, a high voltage pulse is applied to the lamp to establish the arc across the electrodes. The power to the supplied to the lamp is low at this point in order to prevent damage to the electrodes. Ignition of the arc establishes a voltage across the lamp and a carrier gas contained within the lamp is ionized. At this initial start-up stage the temperature of the arc lamp is low. However, the temperature of the arc lamp increases as the gas is ionized and as the lamp warms up power to the lamp is gradually increased. When all of the gas has been ionized the lamp is operating at its brightest capacity and highest temperature.
One method of controlling the heat produced by the arc lamp is to provide a fan to blow cool air over and past the arc lamp. However, a common problem is that the fan may prevent the arc lamp from reaching its full operating temperature by cooling it too much during the lamp start-up period. Typically, the arc lamp and the fan are started simultaneously. The fan operates at full capacity even during the start up period when the arc lamp is operating at a reduced capacity. Operation of the fan at full capacity can delay or may even prevent the arc lamp from reaching its full operating temperature because the cooling effect of the fan is too great. Therefore, it is desirable to control the fan so that it operates at a reduced capacity during the lamp start-up period to allow the arc lamp to reach its full operating temperature.
It is an object of the present invention to provide an arc lamp cooling system that allows the arc lamp to reach its full operating temperature.
It is another object of the present invention to provide a fan control to reduce the cooling effect of the fan during initial start up of the arc lamp.
It is a further object of the present invention to provide a fan control that prevents erratic run-up of the arc lamp.
A portable image projector is provided with a fan having a control system for cooling a metal-halide arc lamp which operates at a very high temperature. Since such portable image projectors are so compact controlling the heat produced by the arc lamps very important, especially during lamp start-up.
The arc lamp cooling system of the present invention includes a fan control to drive the fan at an initially reduced level to allow the temperature of the arc lamp to increase to its full operating temperature after which the fan voltage is increased to its full operating capacity. The fan control includes a microcontroller which is run by software to operate the fan at a reduced voltage over a period of time after which the voltage is increased to operate the fan at full capacity. The voltage at which the fan operates depends upon the temperature of the air at the air intake on as measured by a sensor. The software determines the fan start-up voltage and monitors the time period or periods to increase the fan voltage as a function of the temperature of the air. Power to the fan may be increased in incremental time steps or linearly over a period of time as determined by the microcontroller.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof which proceeds with reference to the accompanying drawings.